Forums :: NEW! Web Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives
Support This Site: Contributors :: Advertise


It is currently Oct Mon 25, 2021 7:00 pm


All times are UTC [ DST ]





Post New Topic Post Reply  [ 4 posts ] 
Author Message
 Post subject: Technics SA-5760 Pop in rebuilt channel
PostPosted: Aug Mon 30, 2021 12:58 pm 
Member

Joined: Apr Wed 13, 2016 1:58 pm
Posts: 364
Location: Bartlett, TN
I received this in bad shape as one channel finals were missing and the other channel didn’t sound great. I was able to recap the unit, repopulate the outputs and replace most of the driver transistors and it sounds fabulous but I still get a random pop from time to time. I traced it down to the protection relay activating but it doesn’t throw an overload lamp but the circuit looks to operate off of offset as well. Placing my scope probes on the feedback to the diff amps (both brand new) and waiting for the pop, one side jumps to 9v, flat lines, and activates the relay. The 9v immediately declines, audio returns, relay pulls back in and all is well for another 20 mins.. strange. Any thoughts? The VAS transistor is still original, one channel finals are original as well as all the current limiter transistors. Resistors have all been checked. I’m kind of at a loss on this one.


Top
 Profile  
 
 Post subject: Re: Technics SA-5760 Pop in rebuilt channel
PostPosted: Aug Mon 30, 2021 2:21 pm 
Member

Joined: Apr Wed 13, 2016 1:58 pm
Posts: 364
Location: Bartlett, TN
Driver board


Attachments:
Screenshot_20210830-082049_Adobe Acrobat.jpg
Screenshot_20210830-082049_Adobe Acrobat.jpg [ 398.2 KiB | Viewed 190 times ]
Top
 Profile  
 
 Post subject: Re: Technics SA-5760 Pop in rebuilt channel
PostPosted: Aug Mon 30, 2021 2:23 pm 
Member

Joined: Apr Wed 13, 2016 1:58 pm
Posts: 364
Location: Bartlett, TN
Relay protection


Attachments:
Screenshot_20210830-082223_Adobe Acrobat.jpg
Screenshot_20210830-082223_Adobe Acrobat.jpg [ 299.55 KiB | Viewed 190 times ]
Top
 Profile  
 
 Post subject: Re: Technics SA-5760 Pop in rebuilt channel
PostPosted: Aug Mon 30, 2021 6:43 pm 
Member

Joined: Apr Wed 13, 2016 1:58 pm
Posts: 364
Location: Bartlett, TN
Looks like I found it. Broken pad on the constant current source was barely making contact.


Top
 Profile  
 
Post New Topic Post Reply  [ 4 posts ] 

All times are UTC [ DST ]


Who is online

Users browsing this forum: dberman51 and 14 guests



Search for:
Jump to:  


































Privacy Policy :: Powered by phpBB